I like the idea of a BBQ guy, we have a few of them around here as well, but the cost is prohibitive. I also went to one event where they hired a bbq truck guy and not only was he expensive...but slow. Real slow, and it ticked people off.
We try to keep our prices super low, 2.00 for a hot dog, 3.00 for a burger, 4 for pulled pork. We also have an arrangement with the seniors who live behind our field and share space with us that they get a free lunch, so we usually give away 40-60 dogs/burgers and drinks. It's a balancing act to project sales/turnout etc, and for the past two events we had just enough for each day and it worked out perfect. Weather and a decent idea of who is coming to the larger events help too. I used to get the food at Costco or Sams, but we have a place that popped up here a few years ago called Aldi's, and there prices are insanely low. We made a pretty penny last year on food sales, over $1000.00 for a two day event, and even at $2.00 for a hot dog we were still making out on the deal, even after the bun and condiments. I did add brauts last year and those went like wildfire. One had cheese in it, the other jalapeno and cheese.